Chapter 1: Matter, Energy, and Measurement – GOB Chemistry Study Notes

Introduction to Matter, Energy, and Measurement

Overview

This chapter introduces fundamental concepts in chemistry, including the nature of matter and energy, and the importance of measurement in scientific study. Understanding these basics is essential for all subsequent topics in General, Organic, and Biological (GOB) Chemistry.

Units of Measurement

SI Base Units

The International System of Units (SI) is the standard for scientific measurement. Each physical quantity has a specific base unit.

• Mass: Kilogram (kg)

• Length: Meter (m)

• Time: Second (s)

• Temperature: Kelvin (K)

• Amount of substance: Mole (mol)

• Electric current: Ampere (A)

• Luminous intensity: Candela (cd)

Metric System Prefixes

Prefixes are used to express multiples or fractions of base units, making measurements more practical for different scales.

• Giga (G): $10^9$

• Mega (M): $10^6$

• Kilo (k): $10^3$

• Deci (d): $10^{-1}$

• Centi (c): $10^{-2}$

• Milli (m): $10^{-3}$

• Micro (\mu): $10^{-6}$

• Nano (n): $10^{-9}$

• Pico (p): $10^{-12}$

• Femto (f): $10^{-15}$

Temperature Measurement

Temperature Scales

Temperature is a measure of the average kinetic energy of particles. The most common scientific scales are Celsius and Kelvin.

• Celsius (°C): Water freezes at 0°C and boils at 100°C.

• Kelvin (K): Absolute zero is 0 K; water freezes at 273 K and boils at 373 K.

• Fahrenheit (°F): Used in some countries; water freezes at 32°F and boils at 212°F.

Conversion formulas:

• $K = \text{°C} + 273.15$

• $\text{°C} = K - 273.15$

Volume Measurement

Metric Units for Volume

Volume is commonly measured in liters (L) and milliliters (mL). The relationships between units are:

• 1 L = 1 dm3

• 1 mL = 1 cm3 = 1 cc

Measuring Volume

Different laboratory glassware is used to measure and deliver volumes of liquids. Some are designed for variable volumes, others for specific volumes.

• Graduated cylinder: Used for variable volumes

• Syringe: Used for variable volumes

• Burette: Used for variable volumes, with stopcock control

• Pipette: Used for specific volumes

• Volumetric flask: Used to hold a specific volume

Density

Definition and Calculation

Density is a physical property defined as mass per unit volume. It is commonly expressed in grams per milliliter (g/mL) or grams per cubic centimeter (g/cm3).

• Formula: $d = \frac{m}{V}$

• To solve for mass: $m = d \times V$

• To solve for volume: $V = \frac{m}{d}$

Volume by displacement is a method used to measure the volume of irregular objects by observing the change in water level.

Uncertainty in Measurement

Exact vs. Inexact Numbers

Exact numbers are defined values (e.g., 12 eggs in a dozen), while inexact numbers are measured and have associated uncertainty.

• Exact numbers: No uncertainty

• Inexact numbers: Some uncertainty, typically in the last digit

Reporting Uncertainty

All measurements have some degree of uncertainty, often indicated by ± notation (e.g., 27 °C ± 1 °C).

Accuracy and Precision

Definitions

Accuracy refers to how close a measurement is to the true value, while precision refers to how close repeated measurements are to each other.

• Accuracy: Proximity to true value

• Precision: Consistency among measurements

Significant Figures

Rules for Determining Significant Figures

Significant figures are the digits in a measurement that are known with certainty plus one digit that is estimated. Rules include:

• All nonzero digits are significant.

• Zeroes between significant digits are significant.

• Zeroes at the beginning are not significant.

• Zeroes at the end are significant if a decimal point is present.

Significant Figures in Calculations

• Addition/Subtraction: Answer should have the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: Answer should have the same number of significant figures as the measurement with the fewest significant figures.

Scientific Notation

Usage and Application

Scientific notation is used to express very large or very small numbers. The format is:

• $a \times 10^n$ where $1 \leq a < 10$ and $n$ is an integer

Move the decimal to create a number between 1 and 10, then count the places moved to determine the exponent.

Dimensional Analysis

Conversion Factors

Dimensional analysis is a method for converting between units using conversion factors derived from equivalence statements.

• Example: 1 in = 2.54 cm

• Conversion factor: $\frac{1\ \text{in}}{2.54\ \text{cm}}$ or $\frac{2.54\ \text{cm}}{1\ \text{in}}$

Metric Conversion and Ladder Method

Converting Units

The ladder method helps determine the direction to move the decimal point when converting between metric units. Move left for larger units, right for smaller units.

Health & Medicine Applications

Dosage Calculations

Dosage is often calculated using conversion factors from medication labels. For example, 325 mg per tablet or 160 mg per 5 mL of solution.

Toxicology

LD50 and Dose Calculations

LD50 is the lethal dose required to kill 50% of test animals, measured in mg/kg or μg/kg. Calculations often involve converting between units and determining the number of doses required to reach a threshold.

Summary Table: SI Base Units

Physical Quantity	Name of Unit	Abbreviation
Mass	Kilogram	kg
Length	Meter	m
Time	Second	s
Temperature	Kelvin	K
Amount of substance	Mole	mol
Electric current	Ampere	A
Luminous intensity	Candela	cd

Summary Table: Metric Prefixes

Prefix	Abbreviation	Meaning	Example
Giga	G	$10^9$	1 gigameter (Gm) = $1 \times 10^9$ m
Mega	M	$10^6$	1 megameter (Mm) = $1 \times 10^6$ m
Kilo	k	$10^3$	1 kilometer (km) = $1 \times 10^3$ m
Deci	d	$10^{-1}$	1 decimeter (dm) = 0.1 m
Centi	c	$10^{-2}$	1 centimeter (cm) = 0.01 m
Milli	m	$10^{-3}$	1 millimeter (mm) = 0.001 m
Micro	\mu	$10^{-6}$	1 micrometer (\mu m) = $1 \times 10^{-6}$ m
Nano	n	$10^{-9}$	1 nanometer (nm) = $1 \times 10^{-9}$ m
Pico	p	$10^{-12}$	1 picometer (pm) = $1 \times 10^{-12}$ m
Femto	f	$10^{-15}$	1 femtometer (fm) = $1 \times 10^{-15}$ m